Despite the onset of the “electronic age,” there is still significant demand for print products. Indeed, commercial print may have annual retail sales totaling more than $700 billion. Print service providers (PSPs) fulfill this demand by printing a vast array of print products, such as photographs and brochures, school course materials, periodicals and books, and advertisements and product packaging. Many of these print products are colored, and costumers desire these colors to be faithfully reproduced.
Printed products are not perfect replicas of the originals. Indeed, average color errors in the range of 3<ΔE<7 (CIE 1976 (L*a*b*)) are routine in commercial print processes run by skillful operators. Less skillful operators or less expensive operations can produce even larger color errors. Moreover, color errors may become more pronounced when market pressures force down production costs. To ensure customer satisfaction while maximizing profits, PSPs may negotiate service license agreements (SLAs) to specify precise color tolerances. The specification of color tolerances may be essential for PSP profit maximization, since a print job with a lower color tolerance can be run on a less accurate printing press or by a less skillful operator.
The standard practice for establishing color tolerances is generally described in ASTM standard D 3134. Standards such as ASTM standard D 3134 may recommend expressing color differences through the CIE 1976 (L*a*b*) color difference equations. More specifically, ASTM standard D 3134 states that color tolerances are preferably set experimentally by classifying specimens visually against a standard, than measuring the specimens standard and plotting the value on a CIE LAB Δa*, Δb* constant lightness (L*≡k,kε[0,100]) plane. For the L* tolerance, D 3134 states that a rough approximation is the lightness difference ΔL* for colors that match the standard in hue and saturation. As such, color tolerances are generally calculated as mean CIE 1976 (L*a*b*) errors. In many cases, this average of errors relates well to customer satisfaction with print job color reproduction. In other cases, however, customers may find color print jobs with similar average error values quite unappealing.